This invention relates to a system for reliably feeding individual sheets from a stack along a transport path including sheets of paper of the type utilized in a facsimile apparatus. In order to reliably feed sheets of paper, it is necessary to contend with a variety of conditions including widely varying humidities. In extremely low humidity conditions, triboelectric charges can make it extremely difficult to reliably separate a sheet-at-a-time from a stack of sheets. Static electricity also creates significant difficulties in feeding individual sheets along a transport path containing nonconducting or plastic components.
In copending application Ser. No. 120,337, which is incorporated herein by reference, a facsimile apparatus is disclosed which requires sheet feeding of facsimile copy paper from a stack in an automatic or unattended manner and feeding of individual sheets along a transport path extending from the stack to a scanning area comprising a rotatable drum. Because this apparatus is intended to operate in an automatic or unattended mode, it becomes extremely important that the sheet feeding occur with reliability since there is no operator present to correct non-feeds and misfeeds of the facsimile paper.
The most commonly utilized facsimile copy paper utilized in apparatus of the type disclosed in the aforesaid copending application Ser. No. 120,337 is electronsensitive paper which is formulated so as to develop a coloration or other marking upon the passage of electric current through the paper. Electrosensitive paper most often used in facsimile applications is of the type described in U.S. Pat. Nos. 3,368,918--Miro et al., 3,511,700--Miro and 3,920,873--Diamond. In such papers, an opaque, nonconducting surface coating of the paper is selectively removed by the passage of a modulated electric current to expose a subsurface, conducting layer having a contrasting color. Electrosensitive paper of this type is particularly difficult to feed from a stack under low humidity conditions because of the build-up of triboelectric charge on the paper.
In ordinary paper, a build-up of static electric charge is avoided by the use of conductive adducts such as metal salts. Alternatively, hygroscopic agents have been employed to absorb the moisture and, thus, to dissipate the charge. Those skilled in the art will recognize that the nature of the electrical conductivity of the various layers of electrosensitive paper is crucial to satisfactory performance. In this regard, it is important to remember that marking on electrosensitive paper is achieved by the selective removal of the opaque, nonconducting outer layer which is accomplished essentially by a process analogous to resistance heating. Any additive to an electrosensitive paper which interfers with the needed resistance and the electrical character of the paper will necessarily adversely affect the marking quality of the electrosensitive paper. For example, one would avoid the use of additives which substantially increase the conductivity of the nonconducting layer. Whereas such additives might be desirable in electrochemical paper wherein conductivity is necessary for the passage of electric current to initiate an electrochemical reaction, increases in conductivity in electrosensitive paper of the type here contemplated, which impair the selective removal of the opaque nonconducting outer layer, are detrimental. See U.S. Pat. Nos. 3,011,918--Silvernail, 3,991,256--Cornier and 4,035,244--Inque wherein electrochemical papers with polymeric quaternary ammonium salts added for conductivity are disclosed.